Ca(2+)-ATPase-driven calcium accumulation in Ustilago maydis plasma membrane vesicles.

Ca2+ transport has been measured across plasma membrane vesicles isolated from cells of Ustilago maydis. This transport was found to be ATP- (or to a lesser extent GTP) and Mg(2+)-dependent. Inconsistent release of Ca2+ from intact vesicles was obtained using the calcium ionophore A23187. However, Ca2+ was released by Triton X-100 in a concentration-dependent manner. Transport was inhibited by vanadate (> 50%) and erythrosin B (about 50%), I50 being about 10 microM for both inhibitors. In the presence of the protonophores CCCP or gramicidin, partial inhibition of Ca2+ transport (about 20%) was observed, but the Ca(2+)-channel blockers, nifedipine, diltiazem and verapamil had no effect, although the latter inhibited proton transport. The results indicate that Ca2+ transport in U. maydis is regulated by a P-type ATPase with similar properties to that found in higher plants.